PowerPoint-Pr

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Hamburg University
The (potential) role of seed ecology in
restoration Germination, seed banks and
establishment Kai Jensen Applied Plant
Ecology University of Hamburg kai.jensen_at_botanik.u
ni-hamburg.de
SER Summer School 2009 Münster University
Department Biology
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Outline

• Introduction
• Germination
• Influence of abiotic factors
• Persistence and Seed Banks
• Primary and secondary dormancy
• Seed bank types
• Dispersal
• Hydrochorous seed transport
• Establishment
• Seed- versus microsite-limitation
• Summary and conclusions

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Changes of fen grassland area and
distribution (1950 2002 Lake Vollstedt,
Northern Germany
Yacoub (2002)
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Seed banks and succession in changing landscapes

• You have only to dig a pond anywhere and you
  will soon have the usual waterplants (Thoreau
  1860)
• Early phase of farm abandonment in New England
• Forest recovery
• You have only to restore the site conditions
  including a proper hydroregime anywhere and you
  will soon have the usual wetland species
• Application of fertilizers led to an
  eutrophication of the landscape
• Widespread land use has greatly homogenized
  formerly dissimilar habitats
• Human development and land-use changes are
  accompanied with habitat fragmentation

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Questions

• Are seed banks and seedling establishment
  important for the conservation and/or restoration
  of wetlands?
• Which factors affect the longevity of seeds in
  the soil?
• Germination requirements?
• Dormancy pattern?
• Seed morphology (weight, shape)?
• Which factors affect hydrochorous dispersal?
• Seed buyoancy?
• Seed production?
• Which factors limit the establishment of species
  in wetlands?
• Seed availability (seed banks, seed dispersal)?
• Microsite availability (gaps, disturbance)?

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Germination Ecology

• Germination is a complex process which includes
  the imbibition of water, an increase in
  respiration activity, the mobilization of
  nutrient reserves and the initiation of growth in
  the embryo. Finally, germination results in the
  bursting of the testa and the extrusion of the
  plumule or radicle.
• How is germination of wetland species affected by
  abiotic factors?
• Temperature and temperature fluctuations
• Light quantity and light quality
• Salinity
• Do germination requirements of individual wetland
  species vary?
• Within individuals?
• Among populations?
• Temporally?

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Temperature and germination

• Methods
• Dry-stored seeds
• Constant tempe-ratures (3 35C)
• Fluctuating tempe-ratures (5/15C 10/25C)
• Diurnal light regime

Patzelt et al. (2001)
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Temperature fluctuations and germination
Carex elongata

• Methods
• Dry-stored seeds
• Daily fluctuating temperatures (amplitudes from 0
  16C)
• Mean temperature 22C

Germination
Carex elata
Schütz (1999)
Amplitude C
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Canopy effects on light quantity and quality

• Above leaf-canopy
• red far-red 1.2

• Below leaf-canopy
• red far-red 0.18

Pons (19xy)
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Light quality and germination
Primula farinosa
Tofieldia calyculata
Maas (1989)
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Seed mass and light-requirement for germination
Jensen Gutekunst (2003)
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Germination in light and in darkness
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Variation of germination within single
inflorescences
25C
Bidens frondosa
Dispersal ability
low
high
Number of germinated seeds
10/20C
Days
Brändel (2004)
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Temporal changes of germination requirements
Silene flos-cuculi
Milberg (1994)
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Germination ecology and zonation in wetlands

• Germination of both species is negatively
  affected by increased salinity
• Interaction between species and salinity
• Spartina has a higher germination percentage
  than Elymus at high salinity
• Elymus has a higher germination than Spartina at
  low salinities

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Summary Germination

• Most (temperate) wetland species germinate at a
  wide amplitude of temperatures, but have an
  optimum between 20 and 30C
• Germination of many wetland species is increased
  by alternating temperatures, which might restrict
  germination to the spring
• Light requirement for germination is higher in
  small-seeded species than in large-seeded ones.
  The light requirement can be interpreted as an
  adaptation against fatal germination in the soil
• Germination requirements vary spatially (within
  inflorescences, among individuals, among
  populations) and temporally (dormancy cycles)

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Seed persisitence and seed banks

• Circumstantial evidence for high longevity of
  seeds (e.g. Nelumbo nucifera dried bed of a
  former lake in NE China germinating seeds were
  radiocarbon-dated to be 1288 250 years,
  Shen-Miller et al. 1995)
• Seed densities in the soil vary greatly (1
  100,000 seeds/m²) between ecosystems
• In general, seed density of individual species
  exponentially declines after it disappeared in
  the vegetation

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Seed bank types

• transient
• seed persistence in the soil for less than 1 year
• short-term-persistent
• seed persistence in the soil for at least 1 year,
  but less than 5 years
• play a role in the maintenance of plant
  populations after a bad year (e.g. poor seed
  set in a dry year)
• long-term persistent
• seed persistence in the soil for at least 5 years
• may contribute to the restoration of destroyed or
  degraded plant communities

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Classification rules for seed bank types
Criteria Presence/absence in vegetation and seed
bank Depth distribution in the soil
Thompson et al. 1997
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Main conclusions of Thompson et al. (1997)

• Grassland species have in general a low seed
  persistence
• Rare species have a lower persistence than common
  ones
• Seed size and shape are good predictors of seed
  persistence

Is that really true??
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Dormancy and seed longevityBurial experiment
with seeds of wetland species
Bromus racemosus
Sanguisorba officinalis
Darkness
Light
Mortality
Germination
Mortality
Date
Jensen (2004)
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Dormancy and seed longevityBurial experiment
with seeds of wetland species
Rhinanthus angustifolius
Pedicularis palustris
100
80
60
Germination
Mortality
40
20
0
Date
Jensen (2004)
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Dormancy and seed longevityBurial experiment
with seeds of wetland species
Germination
Jensen (2004)
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Dormancy and seed longevityBurial experiment
with seeds of wetland species
Jensen (2004)
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Database on seed banks of wetland species

• Seed bank analysis
• 31 wet grasslands in Northern Germany
• Meso- and eutrophic fen grasslands
  (Scheuchzerio-Caricetea, Calthion,
  Lolio-Potentillion)
• Managed and abandoned sites
• Burial experiments
• 45 species of the regional fen flora
• Carex (Schütz 1997, 1998, 1999)
• Regional rare species (Jensen 2001, 2004)
• Asteraceae and Lamiaceae (Brändel 2004)
• Database and literature survey
• Thompson-Database (Thompson et al. 1997)
• 16 seed bank studies (wet grasslands, 143 sites
  in Europe)

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Classification rules for seed bank types
Criteria Presence/absence in vegetation and seed
bank Depth distribution in the soil
Thompson et al. 1997
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Methods Seed bank research

• Classification of species to seed bank types
• Indirect procedure following Thompson et al.
  (1997) All counts, Real seedbank counts
• Direct procedure (burial experiments)
• Calculation of the Longevity-Index (LI, Bekker et
  al. 1998)
• Silene flos-cuculi

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Seed persistence of species groups
LI
ns
a
ab
1.0
ab
ab
ab
b
0.8
a
0.6
ab
ab
ab
ab
b
0.4
0.2
0.0
Kruskall-Wallis-Test
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Habitat specifity, rarity and seed persistence
Low habitat specifity High habitat specifity
Common Rare
1.0
0.8
0.6
Longevity - Index


0.4
0.2
0.0
All counts
Real seedbank counts
Burial experi-ments
All counts
Real seedbank counts
Burial experi-ments
Mann-Whitney-U-Test
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Summary Persistence and seed banks

• Seed banks of many wet grassland species are at
  least short-term persistent
• Rare or endangered wet grassland species do not
  have a lower persistence than common species
• Seed persistence in the soil has been
  underestimated by the methods applied by Thompson
  et al. (1997)
• Seed banks can be an important factor for the
  conservation or restoration of species-rich wet
  grasslands

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Methods Seed dispersal research

• Seed transport by running water
• Seed trapping (Eider 2 years Soomaa 1 summer)
• Recapture experiment (Eider)
• Dispersal of seed mimics (Elbe)
• Modelling of hydrochorous seed transport (Elbe)
• Seed sedimentation during flooding
• Drift-line material (Eider, Soomaa, Elbe)
• Astroturf mats (Eider and Elbe 2002, 2004)
• Dispersal by wind and animals
• Community seed rain (Eider Jensen 1998)
• Seed shadow of wet grassland species
• Seed content of cattle faeces

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Establishment Methods and questions

• Factorial field experiments. Manipulation of
• Seed availability (e.g. sowing, removal of the
  seed bank, exclosure of seed dispersal,
  application of seed-containing drift-line
  material)
• Microsite availabilty (e.g. creation of gaps,
  mowing)
• Is seedling establishment of wetland species
  limited by seed or by microsite availability?
• Is species richness of wetlands limited by seed
  or by microsite availability?

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Sowing experiment (Pedicularis and Rhinanthus)

• 10 blocks per species
• 4 disturbance treatments (control, mowing, small
  gaps, large gaps)
• 4 sowing densities (control, 250, 1250, 5000
  seeds per m²)
• Monitoring of recruitment, survival and
  reproduction

Large gaps
Control
Small gaps
Mowing
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• bienniel
• Seed weight 1.1 mg
• Limited by seed and by microsite availability

• annual
• Seed weight 2.2 mg
• Limited only by seed availabilty

Rasran, Vogt Jensen (2006)
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Field experiment in floodplain grasslands (Soomaa
NP, Estonia)
Drift line
yes
no
no
small gaps
Disturbance
large gaps
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Effects of seed banks and dispersal on wetlands
Drift line
Disturbance
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c
12
b
Species number of recruiting seedlings per 625cm²
a
8
4
0
yes
no
no
small gaps
large gaps
Wanner (2002)
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Effects of seed banks and dispersal on wetlands
Baltic coastal grasslands
without vegetative regrowth
with vegetative regrowth
Number of seedlings per gap
Yes
No
Yes
No
Ludewig (2009)
Seed Bank
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Summary Establishment

• Species not present in the vegetation are in
  general limited by seed availability
  (Pedicularis, Rhinanthus)
• Species with high seed densities in the seed bank
  or with high potential of hydrochorous seed
  dispersal might establish after some kind of soil
  disturbance
• Germination from seed banks might contribute to
  species richness in wetlands (floodplain
  grasslands, coastal grasslands)

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Summary and conclusion

• Many wetland species have persistent seed banks
• Hydrochorous dispersal enables wetland species to
  move large distances and to reach new habitats
• Seed banks and seed dispersal can significantly
  contribute to nature management and restoration
  of wetlands
• Conservation of still existing wetland patches
  should obtain priority
• Restoration success of wetlands depends on site
  conditions, management, spatial and temporal
  aspects

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THM

• You have only to dig a pond anywhere and you
  will soon have the usual waterplants (Thoreau
  1860)
• You have only to restore the site conditions and
  a proper hydrological management anywhere and you
  will soon have the usual wetland species

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Vielen Dank
Postdoc Markus Brändel Antonia
Wanner Technische Mitarbeiter Claudia
Mählmann Jutta Krüger Detlev Böhm Doktoranden
und wiss. Mitarbeiter Kati Vogt Leonid
Rasran Wiebke Schoenberg Sonja Heemann Sigrid
Suchrow Gesine Engels Ebrahem Mohamed Kristin
Ludewig Frauke Müller Sebastian
Schmidt Katharina Schmidt Christian Butzeck
Abschlussarbeiten Sandra Burmeier Anke
Brandt Dirk Lübsen Jessica Hensel Jan
Schwertdfeger Marie Hrach Nina Pohlmann Felix
Heydel Jessica Ehrhardt Jessica
Klepgen Christian Klaus Lotte Korrell Agathe
Schaddach Jule Krause Katharina
Kleiß Friederike Freiwald Sinaida
Albrecht Frauke Brunckhorst Carolin
Gallinat Jana Melanie Hanke Caroline
Thiem Nina Moniac